Mutations

Question 1

what re 4 types of mutations that occur due to DNA replication errors?

Answer 1

base substitution, base insertion, inversion , duplication/ deletion

Question 2

what are outcomes of mutations to DNA?

Answer 2

synonymous mutations cause no change at all
can cause a change in amino acid
can cause a frame shift
can cause a stop codon

Question 3

when will chromosomal inversions not have an effect?

Answer 3

if the inversion occur in non transcribed regions and don’t effect the regulatory or extron regions of the DNA

Question 4

what are the two main types of mutation?

Answer 4

loss of function mutations reduce functionality of the wild type and re normally recessive
gain of function mutations normally result in a novel function e.g. antennapedia mutations in drosophila- they are normally dominant

Question 5

what are the characteristics of mutations?

Answer 5

they are random, not influenced by selection and mutations ar independent to other mutations

Question 6

what are the two views on how mutation causes evolution?

Answer 6

neo darwinist view: evolution via gradual accumulation of advantageous mutations with individually small effects on the fitness of their carriers
catastrophist view: drivers of speciation are mutations of large effect in regulatory genes cause cascade of changes on multiple other genes can cause a large scale phenotypic change

Question 7

what are the four main questions that can be used to investigate mutation?

Answer 7

• what is the rate of mutation
• what are the effects of mutation on fitness?
• is mutation rate itself under genetic control?
• is evolution ever limited by the availability of new mutations?

Question 8

how can you measure the rate of mutation?

Answer 8

the rate of base substitutions per replication cycle, the rate at which new mutations occur per locus per generation, rate at which lethal or deleterious mutations accumulate, rate at which new phenotypic variance is generated by mutations

Question 9

how can you measure the rate of mutation?

Answer 9

• the rate of base substitutions per replication cycle
• the rate at which new mutations occur per locus per generation
• rate at which lethal or deleterious mutations accumulate
• rate at which new phenotypic variance is generated by mutations

Question 10

describe an experiment which measures the rate of visible mutations/ the rate of mutations at a single locus?

Answer 10

have a group of female mice who are homozygous for a recessive coat colour and cross them with a wild type coat male- the progeny will be heterozygous so expect wild type to be the coat colour, if this is not the case then you know that a mutation has occurred at this loci- found that the rate of mutation was 8.4 x10-4 in male gametes and 1.4 x10-4 in female gametes

Question 11

example how an experiment using mice can be used to identify the frequency of mutations

Answer 11

…???

Question 12

if rates of mutation rate at a single loci are so low, why is mutation important?

Answer 12

because there are many many loci and therefore when summed over all genes the input of variation is considerable

Question 13

what experiment can be used to look at the net effect of mutations on fitness?

Answer 13

the balancer chromosome drosophila experiment

Question 14

what experiment can be used to look at the net effect of mutations on fitness?

Answer 14

the balancer chromosome drosophila experiment by Mukai in 1972

Question 15

describe the entire balance chromosome experiment

Answer 15

• the experiment is used to look at the net effect of accumulated mutations on the fitness on a drosophila
• can be used to look at an individual chromosome at a time
• uses a balancer chromosome which contains many inversions and can’t recombine with another chromosome
• cross a male wild type with a female containing the balancer
• the balancer is labelled with curly wing allele and a homo balancer is lethal so you can pick out the chromosome 2+ balancer males from the populations

Question 16

describe the entire balance chromosome experiment

Answer 16

• the experiment is used to look at the net effect of accumulated mutations on the fitness on a drosophila
• can be used to look at an individual chromosome at a time
• uses a balancer chromosome which contains many inversions and can’t recombine with another chromosome
• cross a male wild type with a female containing the balancer
• the balancer is labelled with curly wing allele and a homo balancer is lethal so you can pick out the chromosome 2+ balancer males from the populations
• can then continue with this throughout generations
• the purpose of this is to allow the male chromosome 2 to accumulate mutations that can’t recombine and be lost from the chromosome (want to see net effect)
• the mutations will also not be selected against (if mutation is recessive) so the mutations are hidden from selection
• at each generation you can select a male, make a homo and compare its fitness to the het balancer and look at its fitness
• to check whether the fitness has decreased or increase compare observed phenotypes with expected- expect 1:2 ratio (homo balancer die) if there are more or less homo wt then has been benefcial or deleterious- decrease or increased viability

Question 17

describe the entire balance chromosome experiment

Answer 17

• the experiment is used to look at the net effect of accumulated mutations on the fitness on a drosophila
• can be used to look at an individual chromosome at a time
• uses a balancer chromosome which contains many inversions and can’t recombine with another chromosome
• cross a male wild type with a female containing the balancer
• the balancer is labelled with curly wing allele and a homo balancer is lethal so you can pick out the chromosome 2+ balancer males from the populations
• can then continue with this throughout generations
• do this to many many lines 101
• the purpose of this is to allow the male chromosome 2 to accumulate mutations that can’t recombine and be lost from the chromosome (want to see net effect)
• the mutations will also not be selected against (if mutation is recessive) so the mutations are hidden from selection
• at each generation you can select a male, make a homo and compare its fitness to the het balancer and look at its fitness
• to check whether the fitness has decreased or increase compare observed phenotypes with expected- expect 1:2 ratio (homo balancer die) if there are more or less homo wt then has been benefcial or deleterious- decrease or increased viability

Question 18

what was the outcome of Mukais balancer experiment?

Answer 18

found that at generation 40 there was a 15% reduction in viability and at generation 60 there is a 50% reduction in viability

Question 19

how can the balancer experiment be used to determine whether the catastrophic or neo-darwin theory of how mutations cause evolution

Answer 19

if the neo balancer theory is correct then the balancer experiment will show that all lines behave in the same way as all have similar number of mutations
if the catastrophic theory is right then lines will behave differently as not all lines will have developed mutations - the data supported the neo darwinist pattern

Question 20

what is the problem with the Mukai experiment? how can it be avoided?

Answer 20

when comparing the homo wt to the het balancer you are asusming that the wt has no effect on the phenotype when with the balancer- this is not the case a lot of the time so not good to use this as the standard

Question 21

what is the problem with the Mukai experiment? how can it be avoided?

Answer 21

when comparing the homo wt to the het balancer you are asusming that the wt has no effect on the phenotype when with the balancer- this is not the case a lot of the time so not good to use this as the standard fitness.
instead use a three chromosome assay involving two balancers- find a wild type from a strain which has a homozygous lethal you can use the double balancer as the standard fitness ** (?)

Question 22

what is the equilibrium frequency of an allele?

Answer 22

the balance between selection removing mutations and new mutations forming- causing a tug of war

Question 23

what is an example of genetic elements influencing mutation rate?

Answer 23

In wild type female drosophila there are transposable elements that’s transcription is repressed in the female egg due to P repressor product preventing harm. Therefore, when wild type female is crossed with an ‘M” cell type male from the lab there is no effect as the P type females egg stops the P element being transcribed. but when a P type male is crossed with a M type female, the egg does not contain repressor for P so P transposable elements are transcribed and mutations occur- given inviable offspring

Question 24

what is an example of genetic elements influencing mutation rate?

Answer 24

In wild type female drosophila there are transposable elements that’s transcription is repressed in the female egg due to P repressor product preventing harm. Therefore, when wild type female is crossed with an ‘M” cell type male from the lab there is no effect as the P type females egg stops the P element being transcribed. but when a P type male is crossed with a M type female, the egg does not contain repressor for P so P transposable elements are transcribed and mutations occur- given inviable offspring- present os p elements cause mutation

Question 25

what experiment shows that evolution is limited by the availability of mutations?

Answer 25

compared populations of flies from a dysgenic cross verween p trains versus control strain descended from non dysgenic cross and applie a selection pressure for a hairer phenotype on bristles
the dysgenic cross responds more to seletion- more mutations initially to work with- flies get more bristly sooner.